In the medical field, it is often desirable to measure the thrombotic potential of blood, the tendency of blood to form a clot, and cardiologists have been using such measurements to predict the progression of diseases such as atherosclerosis and heart disease. In recent years, cardiologists have collected data indicating that blood elements play a significant role in heart disease and have concluded that blood clots are the primary cause of the majority of heart attacks.
The accumulating evidence has led to a scientific explanation of the correlation between heart disease and blood clotting processes. More specifically, areas of blood vessels that are covered with fatty plaques become brittle, causing the vessels to crack and fissure as the vessel is stretched. Tiny rifts in the vessel wall expose collagen which attracts formed elements in the blood known as platelets. The platelets aggregate near the rift and adhere to the collagen to restrict blood flow and initiate clotting processes. Cardiologists propose that heart attacks occur when a clot intended to repair a rift in a vessel wall grows too aggressively, blocking the entire passage and obstructing blood flow to the heart.
A significant medical advantage may be gained by using measurements of the clotting process in vitro to predict the likelihood of similar blood clotting processes occurring in vivo. Such measurements can be used to identify patients at greatest risk of heart attacks or strokes by reproducing in vitro the circumstances that lead to these maladies. Early detection of a highly reactive clotting response in a patient's blood permits a physician to treat the patient for excessive blood clotting activity to reduce the patient's susceptibility to heart attack or stroke.
In the past, apparatuses have been devised for evaluating the blood clotting process and associated platelet response of a blood specimen. However, problems with these apparatuses have arisen. Transfer of blood from a patient's circulatory system to the diagnostic apparatus significantly alters the blood elements responsible for clotting, specifically, the blood platelets and plasma protein-clotting factors. When a blood specimen is exposed to a surface other than healthy endothelial tissue, such as glass or other artificial surfaces, blood platelets in the specimen contact the foreign surface and become activated. Blood platelets immediately identify any synthetic blood container as foreign. Likewise, plasma protein-clotting factors, primarily factors VII and XII, become activated upon contact with damaged tissue or a foreign surface to initiate blood coagulation.
These changes significantly affect the transferability of observations on blood in vitro to conclusions about in vivo behavior. Moreover, analysis of the blood specimen using these prior art apparatuses typically requires centrifugation to remove the cellular components of the blood sample, resulting in further alteration of the blood from its state in the bloodstream.
Present procedures for evaluating blood clotting processes attempt to delay the above-described changes by adding anticoagulants, such as sodium citrate, to the blood specimen. Prior to evaluating the clotting potential of the specimen, the effect of the anticoagulant is reversed. However, since the blood was previously exposed to the abnormal surfaces of the blood evaluation device, some clotting factors are partially, or completely, activated, and many of the platelets also have become activated, including undergoing a shape change known as the disk/sphere transformation. Thus, in many respects, the blood specimen has begun the clotting process before diagnostic testing begins, and it becomes difficult to determine the blood specimen's original thrombotic tendency.
As an alternative to treating the blood specimen with anticoagulants, a class of blood evaluation devices has been devised to compensate for any minor activation of blood elements by massively activating the blood specimen immediately upon withdrawal f rom the bloodstream. These devices, generally referred to as whole blood coagulation analyzers, intermix a thrombogenic material, such as ground glass or diatomaceous earth, with the blood specimen to rapidly induce complete activation. Tests using this method of rapid activation, however, produce inconclusive results because clotting occurs too rapidly to distinguish excessively active clotting processes from healthy clotting processes.
Additionally, if blood can be withdrawn and studied in vitro without clotting and without the necessity to mix an anticoagulant with it, it is believed that characteristics other than clotting can be much more accurately observed.
The difficulties suggested in the preceding are not intended to be exhaustive but rather are among many which tend to reduce the accuracy, effectiveness, and physician satisfaction with prior apparatuses and associated methods for testing blood clotting processes. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that such methods and apparatuses appearing in the past will admit to worthwhile improvement.
Accordingly, it is therefore a general object of the invention to provide an apparatus and method for manipulating blood in vitro which will obviate or minimize difficulties of the type previously described.
It is a specific object of the invention to provide a blood extracting and receiving assembly which permits recovery of a blood specimen from a patient for determining the thrombotic tendency of the patient's blood.
It is another object of the invention to provide a blood extracting and receiving assembly which may be used to identify individuals at high risk of maladies resulting from excessive blood clotting activity and to monitor high risk individuals during specific therapy to decrease the clotting activity.
It is still another object of the invention to provide a blood extracting and receiving assembly which maintains a blood specimen in vitro in essentially the same state as found in vivo.
It is a further object of the invention to provide a blood extracting and receiving assembly which alleviates the necessity of adding anticoagulants to the blood specimen and then reversing their effects prior to performing diagnostic testing.
It is yet a further object of the invention to provide a blood extracting and receiving assembly which is self contained, disposable, and economical to manufacture.
It is still a further object of the invention to provide a method for inhibiting activation of blood elements, specifically platelets, and those blood clotting factors which become activated upon exposure to an unnatural surface.
It is yet another object of the invention to provide a method for determining the thrombotic tendency of a blood specimen under sufficiently controlled conditions to permit discrimination between clotting rates which are dangerously high and those that are within an acceptable range.